1. Field of the Disclosure
The present disclosure relates to a light emitting diode and a method of manufacturing the same, and more particularly, to a light emitting diode including a transparent electrode with an improved structure to improve the light extraction efficiency and a method of manufacturing the light emitting diode.
2. Description of the Related Art
A light emitting diode (LED) is formed of a light emitting source using compound semiconductors such as GaAs, AlGaN, and AlGaAs to generate various colors of light. Recently, with the realization of highly efficient red, blue, green and white light emitting diodes using nitride materials having excellent physical and chemical characteristics, the application range of the light emitting diodes has widened. LEDs can be more easily manufactured and controlled than semiconductor lasers and have longer lifetimes than fluorescent lamps, thus replacing fluorescent lamps as illumination light sources of the next generation display devices.
Examples of factors that determine the characteristics of LEDs are color, brightness, and light intensity, which are primarily determined by the compound semiconductor material used for the LED devices. Also, the light generated by an active layer of the LED must be effectively emitted to the outside, and this depends on the structure and the material of a transparent electrode or the package of the LED.
FIG. 1 is a cross-sectional view of a conventional LED. Referring to FIG. 1, the LED includes a sapphire substrate 11, and an n-type semiconductor layer 13, an active layer 15, a p-type semiconductor layer 17, and a transparent electrode 19 sequentially stacked on the sapphire substrate 17.
When a voltage is applied between the n-type semiconductor layer 13 and the p-type semiconductor layer 17, holes from the p-type semiconductor layer 17 and electrons from the n-type semiconductor layer 13 combine in the active layer 15 to emit light. The light is emitted through the transparent electrode 19 to the outside.
However, in the structure illustrated in FIG. 1, light extraction efficiency is low. Light extraction efficiency refers to the ratio of emitted light to generated light in the active layer. The low light extraction efficiency is caused by the difference between the refractive indices of the semiconductor layers and the surrounding material.
FIG. 2 illustrates the optical path of light emitted to the outside in the LED of FIG. 1. When the light emitted by the active layer is emitted to the outside, the light is refracted at a boundary surface 19a between the transparent electrode 19 and the outside. When light travels from the transparent electrode having a high refractive index to the material having a low refractive index at an incidence angle greater than a critical angle, light is totally reflected at the boundary surface 19a. The critical angle θc is given by Equation 1.θc=sin−1(n2/n1)  Equation 1
For example, when the transparent electrode 19 is formed of ITO with a refractive index of 2, and the surrounding material is air with a refractive index of 1, the critical angle is 30°. That is, only light having an incidence angle of less than 30° is emitted to the outside, and light having an incidence angle of 30° or greater is not emitted to the outside, thus resulting in low light extraction efficiency.